In the industrial production of polypeptides it is of interest to achieve a product yield as high as possible. One way to increase the yield is to increase the copy number of a gene encoding a polypeptide of interest. This can be done by placing the gene on a high copy number plasmid, however plasmids are unstable and are often lost from the host cells if there is no selective pressure during the cultivation of the host cells. Another way to increase the copy number of the gene of interest is to integrate it into the host cell chromosome in multiple copies.
The cat-gene (chloramphenicol acetyl transferase) from plasmid pC194 is routinely used as a selective marker in Bacillus transformation. Bacillus licheniformis, however, exhibits chloramphenicol resistance to an extent which hampers the use of chloramphenicol resistance genes for selection of transformants, whether by protoplast transformation, conjugation or electroporation.
Genome sequencing has revealed that several different B. licheniformis strains harbour a sequence in the chromosome which has some homology with known chloramphenicol resistance genes. The homologous sequence is located at position at position 2720850 to 2721500 in the EMBL Bacillus licheniformis ATCC14580 sequence entry, accession number cp000002.